This project is designed to analyze the expression characteristics of 2000 unique cDNAs in selected cell types, developmental states, and environmental conditions. These expression characteristics will help to define the functions of the large number of cloned cDNAs that have no sequence homology to any identified gene. This work is the beginning of a complete expression map of maize cDNAs and will increase our understanding of the global control of gene expression in this and other organisms. Conservation of sequence homology across taxonomic divisions means that genes identified in one organism often have recognizable homologs in other organisms. The consensus gene sequence and expression pattern that is built from such data is a useful addition to our understanding of gene function in all organisms. We have available most of the cloned and partially sequenced cDNAs that will be needed for this project. The additional cDNAs that are required will be isolated at random from our maize leaf cDNA library and them partially sequenced. The sequences will be compared to the DNA database and unique cDNAs will be identified. We will construct eight cDNA probe sets from mRNA isolated from three tissue types (bundle sheath and mesophyll) or organ types (roots), two developmental states (immature and mature leaves), and three environmental conditions (darkened, starved, and refed tissue). We will prepare multiple copies of twenty different cDNA filter sets, each filter of which contains 96 cDNAs. Each probe set will then be hybridized to the complete set of filters (2000 cDNAs) and the extent of hybridization to each cDNA recorded. The expression and sequence data will then be used to determine the expression profile of each cDNA and will help in determining its actual or putative function.